1. Field of the Invention
The invention relates generally to pipe connections, and more particularly to systems and methods for coupling pipes made of dissimilar materials in applications that are subject to large variations in temperature.
2. Related Art
While there are a variety of systems and techniques for making connections between pipes in a variety of applications, many of these are not well suited to transition joints that undergo large variations in temperature. Conventional connections may experience problems in this situation not only because of the very large differences in temperature, but also because of the cycling of these temperature differences. These factors may cause conventional connections to leak or to experience more serious failures.
Transition joints are joints between pipes that are made of dissimilar materials. The problems with conventional connections arise from the fact that the different materials used in transition joints expand and contract at different rates when the temperatures of the connections change. It is common, for example, in cryogenic systems to require the coupling of an aluminum pipe to a steel pipe. A traditional connection would be made by coupling an aluminum flange to the aluminum pipe and a steel flange to the steel pipe. The flanges would then be coupled together with a seal or gasket between them. If this connection were made at a particular temperature and remained at this temperature, it might not experience any problems at all. When the temperature of the connection is changed, however, the two flanges expand or contract at different rates, causing relative movement between them, or between the flanges and the gasket, potentially causing the connection to leak. The expansion or contraction of the flanges could also cause the connection to lose contact pressure between the flanges and the gasket, which could cause or exacerbate leaks.
Attempts to address these problems in the prior art focus on trying to eliminate the mechanical interface between the dissimilar metals. This is typically done in two ways. One way is to use a pair of flanges, each made of a different one of the dissimilar metals, and a gasket that is made of both metals (see FIG. 1.) The gasket has two opposing contact surfaces, each of which contacts a corresponding one of the flanges. The surface of the gasket that contacts the first flange is made of the same metal as the first flange, while the surface of the gasket that contacts the second flange is made of the same metal as the second flange. Because of the difficulty of joining the dissimilar metals using techniques such as conventional welding, the two metals in the gasket are typically explosion welded together.
Another way in which the mechanical interface between the dissimilar metals is eliminated in the prior art is to use a pipe section that is manufactured from both of the metals (see FIG. 2.) Typically, the pipe section consists of a first segment that is made of a first one of the metals and a second segment that is made of a second one of the metals. The two segments are explosion welded together to form a pipe section having one end made of the first metal and the other end made of the second metal. Each end of this pipe section is conventionally welded to the pipe that is made of the same metal in order to make the connection.
Both of the approaches have limitations. For instance, because the dissimilar metals need to be explosion welded, there are limitations on the sizes of the parts having both metals (i.e., the two-metal pipe section and gasket.) As the sizes of the parts increase, the difficulty of making a good weld increases, so the parts must be relatively small (typically no more than 18 inches in diameter.) Further, because of the difficulties involved with explosion welding, there is a perception in the industry that an explosion weld appears may fail even though it appears to be a good weld. In the case of the two-metal pipe section, a failure of the weld could result in a catastrophic failure of the system in which it is used. As a result of the perception that explosion welded connections are not as reliable as conventional connections (e.g., conventionally welded connections or bolted flanges,) connections that employ explosion welding may be less desired by those who might use them.
It would therefore be desirable to provide systems and methods for making connections between pipes made of dissimilar materials (e.g., aluminum and steel) in systems that experience extreme temperatures and/or extreme variations in temperature that may cause conventional connections to leak or fail altogether.